The invention relates to an apparatus for generating a digital video picture, the video picture being composed of a plurality of components, in particular main picture and secondary picture.
The invention is based on an apparatus for generating a digital video picture of the generic type of the independent claims 1 and 2. In video technology, it is known to provide so-called subpicture decoding devices, for example in a DVD playback device, for displaying for example subtitles on the screen of a television set. DVD playback devices of this type are already commercially available and contain the abovementioned subpicture decoding device. However, such subpicture decoding devices also come into consideration in the context of receivers for digital television (set-top box). The abovementioned subpicture decoding units are already commercially available and correspondingly known to the relevant person skilled in the art. A description of the subpicture decoding devices is found, moreover, in the DVD standard DVD Specifications for Read-Only Disc, Part 3, Video Specification, Version 1.0, Aug. 96, 5.4.3 Sub Picture Unit (SPU). A detailed description of such subpicture decoding devices is also found in EP-A-0 725 541.
In the case of the abovementioned electronic equipment (DVD playback device and set-top box), it is customary, as in the case of other equipment appertaining to consumer electronics, too, to insert status information from the respective equipment in the output video picture. In addition, the use of so-called on-screen display menus (OSD) for operational guidance is widespread. Such menus relate for example to the setting of the volume in the case of a television set with the aid of a displayed bar indicator, the setting of balance, colour contrast, brightness, etc. in the case of a television set, the selection of a programme location by means of a displayed table with regard to the stored TV programme locations in the case of a television receiver, specific menus for the programming of a video recorder and so on. In order to generate such OSD menus or else status displays, use is nowadays usually made of specialized microcontroller circuits with internal or external ROM and RAM memories. These circuits are usually designed in such a way that the dot matrix-like pattern for each displayable character is stored in the ROM memory. Graphics characters with the aid of which, for example, the corresponding bar charts can be composed may also be mentioned as displayable characters. For an OSD menu, the requisite character codes are then transferred to a character generator, which removes the associated dot matrix data from the ROM and generates the associated RGB signals at the correct locations in the picture and inserts them in the picture. The solution can also be configured for equipment with digital signal processing (including digital frame store) in such a way that the pixel data are generated individually by the character generator and written to the frame store at the corresponding locations.
If such a conventional OSD circuit is additionally used for the insertion of status information and menus for operational guidance in the abovementioned equipment (DVD playback device, set-top box, etc.), then the problem arises that not only the already mentioned subpicture decoding unit must be implemented with hardware outlay but also the OSD circuit. This causes increased costs in the development of the equipment since it is necessary to develop and adapt two very different circuits for the insertion of subpictures/secondary pictures.
An inventive arrangement reduces costs associated with providing circuitry for generating operational menus and status information in equipment with an integrated subpicture decoding unit. In a first inventive arrangement an existing subpicture decoding unit is, in addition, advantageously used for generating status information or operating menus. To this end, it is provided that the equipment has a storage device in which the data for the displayable status information or operating menus are stored in a correspondingly coded form. The data for such secondary pictures are loaded into the subpicture decoding unit, following a request by means of a corresponding command, and are then decoded in the decoding unit after the decoding of data for a possibly activated, different subpicture (for example subtitles) has been stopped. In the case of this solution, then, the insertion of subtitles is suppressed and, instead, the secondary picture with the status information or the operating menus is displayed. However, this is not necessarily disadvantageous since the user generating the exemplary menu command will wish to view the operating menu in any case.
In a second solution according to the invention, a second subpicture decoding unit for the status information and operating menus is provided in addition to the subpicture decoding unit for the outputting of the subtitles. Both subpicture decoding units may be constructed similarly because the data for the operating menus and status information are coded according to the same coding rules as the data for the subtitles. Although it is necessary to provide a second subpicture decoding unit in this solution, the implementation outlay is considerably reduced since both subpicture decoding units are constructed similarly. The advantage of this solution consists principally in the fact that subtitles and operating menus and/or status information can be inserted simultaneously in the video picture. This is advantageous particularly when status information such as, for example, time of day, playing time, date, remaining playing time, etc. are to be added to the picture.
In a third solution according to the invention the two separate subpicture decoding units of the second solution are combined to form a common decoding unit. However, this presupposes that the subpicture decoding unit has sufficient memory to store the data of two different subpictures and to process the data successively with correct timing throughout the duration of a video frame or field.
The following holds true for all three solutions: if only simple OSD menus are intended to be displayed, for example the insertion of simple symbols for the display of the operating mode, it is not absolutely necessary to load the data of the subpicture units into the subpicture decoding units if the subpicture decoding devices are designed in such a way that they can decode the associated data directly from the non-volatile memory (ROM).
The solutions according to the invention have the following advantages in addition to the advantages already mentioned. The data for a subpicture contain, firstly, the so-called bit map data for the subpicture and, secondly, the so-called display control command sequences. By virtue of the fact that bit map data for the subpictures are used, practically any desired configurations are easily possible for the OSD menus. It is also advantageous that the bit map data are run length coded. This saves memory space.
The fact that the subpicture decoding unit decodes the bit map data in a line-oriented manner means that it is not necessary to buffer-store the entire decoded subpicture in a memory. This also saves memory space.